Gas discharge tube is a gap-type lightning protection component that has been widely used in communication system lightning protection. Discharge tubes are often used in the front stage or first two stages of multi-level protection circuits to discharge lightning instantaneous overcurrent and limit overvoltage.
Commonly used gas discharge tubes include diode discharge tubes and triode discharge tubes. Most of its packaging materials are ceramics, so they are called ceramic discharge tubes.

GDT selection strategy, a must-read guide for beginners

1) The selection of DC breakdown voltage should refer to the working voltage of the circuit, and its voltage value should be greater than the maximum working voltage of the protected line.

2) The pulse breakdown voltage should consider the surge test level. Generally, the rise time of the surge test waveform is a pulse waveform of microseconds, such as 8/20-μs current wave and 10/700-μs voltage wave, which is different from GDT pulse breakdown voltage measurement. The voltage rise rate is 1000-V/μs, which is an order of magnitude. For example, if a 10/700-μs waveform is used to test 4000-V, the pulse breakdown voltage of the GDT must be less than 4000-V, so that the GDT can be turned on during the test.

3) Due to the large error in breakdown voltage of GDT, it is generally not used in parallel in the circuit;

4) GDT is a switch overvoltage protection component. The voltage is low after it is turned on and cannot be used alone for higher power line protection. MOV or PTC can be connected in series with GDT to limit freewheeling problems;

5) The packaging form should be selected according to the circuit design layout. The size of the GDT package reflects its level of protection. The larger the package, the stronger its ability to withstand surge current and the higher the protection level.

How much do you know about ceramic gas discharge tubes?

Ceramic gas discharge tube, GDT (Gas Discharge Tube), is a sealed device composed of one or more discharge gaps filled with inert gas. Ceramic gas discharge tubes can withstand surge currents of up to hundreds of thousands of amps. The specific electrical characteristics are closely related to factors such as gas type, internal electrode structure, gas pressure, and manufacturing process. Features of ceramic gas discharge tube:

>> Low junction capacitance, the junction capacitance of most GDTs is less than 2-pF, and the junction capacitance of extra-large flow GDTs is tens to tens of pF;

>> Large flow rate, the flow range of Futurewafer's GDT monomer 8/20-us waveform is 1-KA to 5-KA;

>> High insulation resistance, generally above 1-GΩ, not easy to age and has high reliability;

>> DC breakdown voltage range is: 75-V to 6000-V; Pulse breakdown voltage range is 600-V to 7800-V;

>> Various packaging forms, including chip plug-in, two-pole, three-pole, round, and square electrodes, can meet different application needs;